Flow regulation vent

ABSTRACT

A flow regulation vent for use in controlling a vent flow of washout gas in a system for supplying breathable gas pressurized to within a therapeutic pressure range above atmospheric pressure to a patient in the treatment of a sleep disordered breathing condition is disclosed. The flow regulation vent may include a housing having at least one vent orifice and at least one fixed bleed orifice; and a flap configured to regulate the vent flow of washout gas through the at least one vent orifice, wherein the at least one fixed bleed orifice is not covered by the flap in any position and the flow regulation vent provides a minimum vent flow independent of the position of the flap.

This application is a continuation of U.S. patent application Ser. No.15/001,521, filed Jan. 20, 2016, pending, which is a continuation ofU.S. patent application Ser. No. 13/891,237, filed May 10, 2013, nowU.S. Pat. No. 9,278,186, which is a continuation of U.S. patentapplication Ser. No. 10/433,980, filed Jun. 10, 2003, now U.S. Pat. No.8,439,035, which is the U.S. national phase of International ApplicationNo. PCT/AU01/01658, filed Dec. 21, 2001, and claims priority to U.S.Provisional Application No. 60/257,171, filed Dec. 22, 2000, the entirecontents of each of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a vent valve apparatus for use with asystem for supplying breathable gas pressurized above atmosphericpressure to a human.

The invention has been developed primarily for use in controlling theventing of washout gas in a continuous positive airway pressure (CPAP)gas delivery systems used, for example, in the treatment of obstructivesleep apnea (OSA) and similar sleep disordered breathing conditions. Theinvention may also be used in conjunction with suitable mask and gasdelivery systems for the application of assisted ventilation treatment.

The term “mask” is herein intended to include face masks, nose masks,mouth masks, appendages in the vicinity of any of these masks and thelike.

BACKGROUND OF THE INVENTION

Treatment of OSA by CPAP gas delivery systems involves the continuousdelivery of air (or breathable gas) pressurized above atmosphericpressure to a patient's airways via a conduit and a mask. CPAP pressuresof 4 cm H₂0 to 30 cm H₂0 are typically used for treatment of sleepdisordered breathing due to OSA and/or central apnea, depending onpatient requirements.

Treatment pressures for assisted ventilation can range up to 32 cm H₂0and beyond, depending on patient requirements.

For either the treatment of OSA or the application of assistedventilation, the pressure of the gas delivered to patients can beconstant level, bi-level (in synchronism with patient inspiration andexpiration) or automatically adjusting in level. Throughout thisspecification the reference to CPAP is intended to incorporate areference to any one of, or combinations of, these forms of pressuredelivery. The prior art method for providing CPAP treatment includes avent for gas washout of the gas flow. The vent is normally located at ornear the mask or in the gas delivery conduit. The flow of gas throughthe vent is essential for removal of exhaled gases from the breathingcircuit. Adequate gas washout is achieved by selecting a vent size andconfiguration that will allow a minimum safe gas flow at the lowestoperating CPAP pressure, which typically can be as low as, around 4 cmH₂0 for adults and 2 cm H₂0 in pediatric applications.

Existing vent configurations include single or multiple holes, foam orother diffusers, slots and combinations thereof. A reference herein to avent may be understood to include a reference to one or more holes, foamor other diffusers, slots or any combination of them.

It is obviously desirable for a CPAP system to have as wide a pressurerange as is feasible in order that a standard configuration mayadequately provide the unique treatment require by a variety of users.Increasing CPAP pressure results in more gas passing through the ventwhich in turn creates more noise. Existing prior art vents can produceexcessive noise when CPAP pressures are raised above about 4 cm H₂0.This noise can adversely affect patient and bed-partner comfort. Athigher pressures, existing vents are also inefficient as they allow moregas through the vent than is required for adequate exhaust gas washoutand thereby require the flow generator to provide more flow than isnecessary in order to maintain the required treatment pressure. Further,where treatment gas is being supplied, such as oxygen, surplus treatmentgas is vented and thereby wasted unnecessarily. A similar waste occurswhere the supplied gas is humidified.

The flow of gas from the gas delivery system through the vent toatmosphere creates noise as the delivered gas, and upon expiration thepatient expired gas including C0₂, passes through the vent toatmosphere. A CPAP system must have a rate of flow through the vent toatmosphere that ensures a clinically undesirable level of expired gas isnot retained within the breathing circuit (i.e. within the gas supplyconduit and mask chamber). This retention occurs as a result of theexhaled gas not being vented to atmosphere during the exhalation phaseof respiration but rather moving down the gas conduit towards the flowgenerator or accumulating within the mask chamber dead space. Anadequate flow of gas to atmosphere may be achieved by selecting thesuitable vent size for the clinically desirable pressure treatment rangeand volume of gas made available by the flow generator to achieve thedesired treatment pressure range. Typically this selection involves acompromise being struck between the choice of a vent size that issufficiently large to achieve an adequate flow rate at the low end ofthe pressure range and yet cause no greater than an acceptable noiselevel as the pressure increases through the pressure range. In addition,a large vent which would allow for a generous wash out flow rate at thelow end of the pressure range will dictate that the flow generator musthave adequate capacity to provide the flow necessary to achieve thedesired pressures higher in the pressure range. In short, where the ventsize is chosen to deliver a quiet gas wash out flow rate at the higherpressure levels of the pressure range it may be inadequate to allowacceptable wash out flow at the desired lowest end of the pressurerange. Also a vent with sufficient size to achieve an adequate wash outflow rate at pressures low in the pressure range tend to generateunacceptable noise at the desired higher end of the pressure range. Inaddition the choice of a larger vent dictates that the source of gashave capacity to deliver the requisite flow rates for the higherpressure levels and as such the gas source will tend to consume morepower and generate louder noise and require additional noise attenuatingfeatures so as to keep the total noise within acceptable limits.

Because of the constraints on CPAP system design arising from the vent achoice may be made to limit the lower or upper achievable pressure i.e.for a given upper or lower pressure the delta P between that pressureand the other extreme of the range may be inconveniently constrained.The delta P would be chosen so as to achieve the desired aims ofadequate wash out of exhaled gas at the lowest end of the pressure rangewhile capping the noise generated and power consumed at the higher endof the pressure range. Such limitations on the choice of upper or lowerpressures and the delta P can seriously confine the usefulness of CPAPsystem as it is desirable for a standard configuration to have thecapacity to deliver the widest pressure range so as to be capable ofmeeting the clinical requirement of as many users as possible.Achievement of this aim is particularly significant where the CPAPtreatment involves the operation of a control algorithm that varies thepressure delivered to the user during the period of treatment (forexample on a breath-by-breath basis between two or more pressures or ina more complex manner during the period of treatment). Similarly acomputer controlled CPAP system that varies the pressure during theperiod of treatment in accordance with a control algorithm will includeoperating parameters which reflect the vent characteristic of thebreathing circuit. Because of this it can be undesirable to change froma mask specified for the control algorithm for concern that the new maskshould introduce a vent characteristic which is not within the operatingparameters of the control algorithm. This inability to change masksbecause of the accompanying introduction of unknown or incompatible ventcharacteristics can be adverse to patient compliance with CPAPtreatment. This is because a patient may only tolerate CPAP treatmentwhere it is delivered through a particular mask and that mask isincompatible with the prescribed CPAP system control algorithm.Accordingly another aim of the present invention is to provide for amethod of configuring and making a vent which can change the ventcharacteristic of a mask so that the mask may better comply with theoperating parameters of a CPAP system control algorithm.

A further aim of the present invention is a method and apparatus for asystem of venting which creates a vent having a flow area which varieswith changes in pressure occurring at part of or the whole of a CPAPsystem pressure operating range.

It is known in the art for a CPAP system breathing circuits to includevalves that restrict or block venting to atmosphere in givencircumstances.

U.S. Pat. No. 5,685,296 to Zdrojkowski discloses a Flow Regulating Valveand Method. In the first embodiment, a rigid insert 52 having a centralaxial opening 54 is connected to a resilient diaphragm 42. As gas supplypressure increases, the diaphragm 42 flexes toward valve body member 38and opening 54 moves over a body portion 70 of regulating pin 62,thereby decreasing the flow area between opening 54 and regulating pin62 and maintaining a relatively constant gas flow rate even at thehigher gas pressure. In additional embodiments, gas supply pressure isused to move flexible diaphragms 42′ and 42″ toward respective valvebody walls, thereby decreasing the gas flow areas between the respectivediaphragms and the valve body walls and preventing higher gas flows athigher gas pressures.

U.S. Pat. No. 6,006,748 to Hollis discloses a Vent Valve Apparatus whichis adapted to progressively restrict a flow area of a washout vent asthe pressure of the gas supply increases. In two embodiments disclosedtherein, a flexible diaphragm 20 sensitive to the pressure of the gassupply is connected by a rigid wire rod 23 to a conical plug 18positioned in a conical orifice 15. As the pressure of the gas supplyincreases, the diaphragm 20 bulges outward. This moves the rod 23 andconical plug 18 such that the conical plug 18 is drawn into the orifice15, thereby decreasing the flow area of the vent between the plug 18 andorifice 15 and restricting the flow of gasses through the vent. In athird embodiment, an aerodynamic wing 30 replaces the diaphragm 20 andmoves the conical plug in relation to gas flow past the aerodynamicsurfaces of the wing.

While each of these references discloses embodiments that restrict gasflow as the pressure of the gas supply increases, there is a desire toprovide a flow regulation vent that is simpler and cheaper tomanufacture while providing the opportunity to have the flow through thevent vary as the pressure varies in a manner that is not limited toachieving a constant flow rate.

These valves are generally known as non-rebreath or anti-asphyxiavalves. An example of a non-rebreath valve is U.S. Pat. No. 5,438,981 toStarr et al. for an Automatic Safety Valve And Diffuser For Nasal And/OrOral Gas Delivery Mask which includes a valve element 32 that can pivotbetween a first position and a second position to allow inflow into amask from either a gas flow generator or the atmosphere. The safetyvalve does not restrict gas flow as the pressure of the gas supplyincreases.

Other examples of safety valves can be found in U.S. Pat. Nos.5,896,857, 6,189,532 (Hely/Lithgow assigned to ResMed Limited) and WO00/38772 (Walker et. al assigned to ResMed Limited).

An embodiment of the vent of the present invention could also serve as anon-rebreath or antiasphyxia valve.

SUMMARY OF THE INVENTION

The present invention is a flow regulation vent for regulating flow froma pressurized gas supply. The vent includes a fixed portion adapted toengage a gas supply conduit and a spring force biased movable portionconnected by a hinge to the fixed portion and flowingly connected to thepressurized gas supply. The fixed portion includes a gas flow orifice.The movable portion is pivotally movable between a relaxed position anda fully pressurized position. At a specified minimum operating pressure,the movable portion is pivoted by the spring force away from the fixedportion to the relaxed position to establish a first gas flow areabetween the movable portion and the gas flow orifice. At a specifiedgreater operating pressure, the pressurized gas offsets the spring forceto pivot the movable portion to the fully pressurized position adjacentthe fixed portion to establish a minimum gas flow area between themovable portion and the gas flow orifice. In a preferred embodiment, thefixed portion and the movable portion are unitarily formed from a singlepiece of material, such as a sheet of stainless steel or a sheet ofplastic.

By tuning the operating characteristics of the flow regulation vent(i.e. the size of the gas flow orifice at a given pressure), the flowrate curve (being the flow through the vent) can be tailored to berelatively constant across a specified operating pressure range or to bea non-constant flow curve over a specified operating pressure range.

In a further embodiment, the flow regulation vent can operate as a flowmeter by including a strain gauge mounted between the fixed portion andthe movable portion for measuring the position of the movable portionand providing an indicator of flow through the vent. The signalgenerated by the strain gauge transducer will be used with the pressureto determine the flow of gas through the vent.

In an alternative embodiment of the present invention the flowregulation vent includes a flexible flap portion having a portionengaging or attached to a fixed housing so that a free portion of theflap can move within a given range with respect to the housing. One sideof the flap is exposed to an interior of the mask shell or gas flowconduit that is pressurized when the CPAP system mask is in use andanother side is positioned toward an atmosphere side of the vent.

The housing includes a vent orifice positioned beneath the free portionof the flap with a portion of the housing surrounding the vent orificebeing curved. While flexible, the flap has a level of natural rigiditythat will provide a spring resistance against bending of the flap. In arelaxed state, the free portion of the flap will leave the vent orificeuncovered and a gas flow area between the vent orifice and the flap willbe at a maximum. When the CPAP system is in use a force will act againstthe spring resistance of the flap and the free portion of the flap willtend to move toward the vent orifice. As the free portion of the flapmoves closer to the vent orifice with increasing mask pressure, itfollows the curved surface of the housing, progressively closing thevent orifice and reducing the gas flow area between the vent orifice andthe flap. The interaction between the increasing mask pressure anddecreasing gas flow area acts to reduce the gas flow rate through thevent as compared to the flow that would be achieved with a vent ofconstant gas flow area.

An alternative embodiment of the flow regulation vent of the presentinvention opens an auxiliary exhalation vent orifice during exhalationto allow higher exhalation gas flow to atmosphere. An embodiment mayalso include a non-rebreath valve or anti-asphyxias valve function thatreduces or eliminates exhaled gas being retained in the gas circuitafter the end of exhalation. These embodiments serve the desired aim ofeliminating or at least reducing the occurrence of a user rebreathingexhaled gas.

In yet another embodiment the vent of the present invention could beconfigured so as to facilitate the retention in the mask of a desiredlevel of exhaled breath including CO₂. The desired level of retentionwould be directed towards augmenting a prescribed treatment, where someCO₂ retention may serve to counter the patient's own excessiveexhalation of CO₂.

The flow regulation vent of the present invention is simple andinexpensive to manufacture but provides effective, easily tailored flowregulation. The flow regulation vent reduces operating noise of the CPAPsystem by reducing the volume of gas flow required from the flowgenerator at high pressures, as well as thus reducing the work output ofthe flow generator. The vent also reduces rebreathing of CO₂ and otherexhaled gas and provides for faster air pressure rise time, increasingthe effectiveness of the CPAP system and patient compliance with CPAPtreatment.

The invention will now be described in detail in conjunction with thefollowing drawings in which like reference numerals designate likeelements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of the flow regulation valve of the presentinvention;

FIG. 2 is a side plan view of the flow regulation valve of FIG. 1 in afully pressurized position;

FIG. 3 is a side plan view of the flow regulation valve of FIG. 1 in arelaxed position:

FIG. 4 is an exploded perspective view of the flow regulation valve ofthe FIG. 1 in combination with base and cover:

FIG. 5 is a side plan view of the exploded view of FIG. 4:

FIG. 6 is a sectional view taken along section line 6-6 in FIG. 5:

FIG. 7 is a side plan view of the flow regulation vent of FIG. 1attached to a shell of a breathing mask;

FIG. 8 is a side plan view of the flow regulation vent of FIG. 1attached to a gas supply tube connecting a shell of a breathing mask toa pressurized gas supply;

FIG. 9 is a sectional view of an alternative embodiment of the flowregulation vent of the present invention;

FIG. 10 is a graph of flow rate vs. pressure of a mask utilizing thevent of the present invention in comparison to conventional masks:

FIG. 11 is a perspective exploded view of an alternative embodiment ofthe present invention:

FIG. 12 is a sectional view of an alternative embodiment of a flowregulation vent of the present invention;

FIG. 13 is a chart showing the relationship between a radius ofcurvature and a deflection angle for a given pressure at which a flap ofthe embodiment of FIG. 12 completely closes the vent:

FIGS. 14 and 15 are perspective views of an alternative embodiment of aflow regulation vent of the present invention:

FIG. 16 is a sectional view of the embodiment of FIGS. 14 and 15;

FIG. 17 is a perspective view of an alternative embodiment of a flowregulation vent of the present invention:

FIG. 18 is a sectional view of the embodiment of FIG. 17;

FIG. 19 is a perspective view of an alternative embodiment of a flowregulation vent of the present invention:

FIG. 20 is a sectional view of the embodiment of FIG. 19:

FIGS. 21-23 are perspective views of alternative embodiments of flowregulation vents of the present invention;

FIG. 24 is a perspective view of an alternative embodiment of a flowregulation vent of the present invention connected to a mask shell:

FIGS. 25 and 26 are perspective views of an alternative embodiment offlow regulation vents of the present invention;

FIG. 27 is a sectional view of the embodiment of FIGS. 25 and 26;

FIG. 28 is a sectional view of a cover and mounted flap of a vent of aconfiguration similar to the embodiment shown in FIGS. 25-27, with theflap shown in three different positions based on mask pressure exposedto the flap;

FIG. 29 is a perspective view of a flow regulation vent similar to theembodiment of FIGS. 25-27 connected to a mask shell:

FIG. 30 is an exploded view of an alternative embodiment of a flowregulation vent of the present invention:

FIG. 31 is a perspective view of the embodiment of FIG. 30:

FIG. 32 is a sectional view of the embodiment of FIG. 30;

FIGS. 33 and 34 show two charts comparing the flow performance of astandard ResMed™ Mirage® mask with a ResMed™ Mirage® mask utilizing avent according to one of the embodiments of FIGS. 12-32;

FIG. 35 is a flow generator side perspective view of an alternativeembodiment flow regulation vent of the present invention;

FIG. 36 is a mask side perspective view of the vent of FIG. 35;

FIG. 37 is a flow generator side perspective view of a housing of thevent of FIG. 35;

FIG. 38 is a side perspective view of the housing of FIG. 37;

FIG. 39 is a front view of a flap of the vent of FIG. 35;

FIGS. 40-42 are partial sectional views of the vent of FIG. 35 showinggas flow through the vent during different stages of operation;

FIG. 43 is an exploded perspective view of an alternative configurationof the vent of FIG. 35;

FIG. 44 is an exploded perspective view of the vent of FIG. 43 incombination with a mask elbow joint;

FIG. 45 is a perspective view of the vent of FIG. 43 positioned in amask elbow joint; and

FIG. 46 is a partial sectional view of a modification of the embodimentof FIG. 12:

FIG. 47 is a partial sectional view of a modification of the embodimentof FIG. 12;

FIG. 48 is a partial top plan view of a modification of the housing ofthe embodiment of FIG. 12; and

FIG. 49 is a partial sectional view of a modification of the embodimentof FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A flow regulation vent 10 is shown in FIGS. 1-3, and, in thisembodiment, is circular. The flow regulation vent 10 is constructed froma unitary sheet of material and includes a movable portion 12 pivotallyattached at one end to a fixed portion 14 by unitary hinge 16. Movableportion 12 has an outer perimeter 18, which, in the embodiment shown, issubstantially circular. Fixed portion 14 includes an orifice 20, which,in the embodiment shown, is also substantially circular and which isslightly larger in diameter than the diameter of the outer perimeter 18to provide a gap 22 therebetween when the movable portion is in a fullypressurized position. See FIG. 2, which shows a side view of the vent 10when in the fully pressurized position. Movable portion 12 canoptionally include one or more bleed orifices 24 and fixed portion 14can optionally include one or more bleed orifices 26.

FIG. 4 shows the flow regulation vent 10 in an exploded perspective viewin combination with a base portion 30 and a cover 40. The base portion30 can be an integral part of a breathing mask shell 32 for covering themouth and/or nostrils of the patient 50 (see FIG. 7) or can be anintegral part of a gas flow tube or conduit 34 that connects the shell32 to a pressurized gas supply (see FIG. 8). Alternatively, the baseportion 30 can be a separate unit attachable to the shell 32 or tube 34.The base portion 30 includes a support ring 36 that supports an outerperiphery of the vent 10 and one or more orifices 38 for connecting thevent 10 to the pressurized gas supply. Alternatively, the bottom of thebase portion can be open to the mask shell or gas conduit, but theutilization of a floor with orifices 38 is preferred when the vent 10 ismounted to the mask shell to reduce access to the vent 10 from theinterior of the mask shell and prevent accidental damage to the vent 10from the interior of the mask shell. The cover 40 fits over and isconnected to the base portion 30 to fix the vent in place. The coverincludes one or more orifices 42 for venting gas to the atmosphere fromthe vent 10. The number, size, positioning and shape of the orifices 38and 42 can be altered as appropriate for the specific application toalter gas flow and noise levels. In the preferred embodiment, cover 40has 18 orifices of 1.2 mm diameter to provide a level of noisereduction. Alternatively, the cover 40 can be made of a wire mesh orother mesh such as in accordance with co-pending U.S. patent applicationSer. No. 09/570,907 filed May 15, 2000 presently unpublished thecontents of which are incorporated herein by reference. The cover can beattached to the base portion in any known manner, including snap-fit,screw-on or glued. The snap-fit or screw-on connection is preferredsince this provides for ease of cleaning or replacing the vent 10. FIGS.4 and 5 show projections 44 on support ring 36 that can engage anindentation 46 on the interior of the cover 40 to provide a snap-fit.

As can be seen in FIGS. 5, 7 and 8, in the relaxed position, the movableportion 12 of vent 10 (shown in phantom) is pivoted away from the fixedportion 14 toward the mask shell 32 or gas supply tube 34, i.e. towardsthe pressurized gas supply and away from the atmosphere.

The operation of the flow regulation vent 10 will now be described. Atthe minimum safe gas flow at the lowest operating CPAP pressure of, say,2-4 cm H₂0, the movable portion 12 is biased by the force from thespring hinge 16 into a relaxed position pivoted away from the fixedportion 14 and toward the pressurized gas supply. See FIGS. 3, 7 and 8.This provides a maximum gas flow area between the movable portion 12 andthe orifice 20. Thus, at such a low pressure, the flow area is maximizedfor allowing gas to easily vent from the mask shell 32 to theatmosphere. This design can also act as an anti-asphyxia valve designedto be open with a large flow area to the atmosphere at low or nopressure. For instance, if the flow generator stops working due to amalfunction, the vent 10 remains open, allowing the patient to continuebreathing while reducing the risk of asphyxiation, or even theperception thereof, by the patient. A specific flow area is required forthe achievement of an anti-asphyxia effect that is usually larger thanwould be necessary to achieve the lower end of the pressure range duringnormal operation. Therefore, an antiasphyxia embodiment can be designedto include an even larger flow area that is fully exposed and providesan adequate anti-asphyxia effect when there is no pressure in the system(as is the case when there is a failure of power or the flow generatorand when the anti-asphyxia effect is required). That specific flow areawould then close somewhat when the CPAP system is operating as intendedat the lowest/lower pressure range and from there the movable portioncontinues to reduce the flow area as designed with increasing pressure.

However, as CPAP pressure increases, a force acts on the surface of themovable portion 12 to counteract the force of the spring hinge 16 andmove the movable portion 12 toward the fixed portion 14. This actioncauses a continuous reduction in the gas flow area between the movableportion 12 and the orifice 20. Once the maximum designed operatingpressure is reached, the gas flow area between the movable portion 12and the orifice 20 is at a minimum. A further increase in pressure willnot lead to a further reduction of the gas flow area. In the preferredembodiment, the minimum gas flow area is achieved when the movableportion 12 and the fixed portion 14 are essentially coplanar, i.e. liein the same plane, and the gap 22 between the orifice 20 and the outerperiphery 18 of movable portion 12 is minimized. See FIG. 2.

Thus, by the present invention, a gas flow area for allowing gas toescape from the CPAP system to atmosphere is reduced as the pressure ofthe gas supply increases. In this way, the total flow rate for gas fromthe CPAP system is reduced (as compared to a fixed gas flow area vent)even though the pressure of the gas is increasing. Through appropriatetuning of the flow regulation vent 10 within a specified operatingpressure range of the CPAP system, a desired flow rate curve can beobtained, including a flow rate curve that is substantially flat acrossthe specified operating pressure range. In alternative embodiments, theflow regulation vent 10 can be tuned to provide an increasing flow ratecurve or even a decreasing flow rate curve, if the specific applicationwarrants such, or even different combinations of flat, rising andfalling curves at different segments within the specified operatingrange.

The flow regulation vent 10 can be tuned to deliver differing flow ratecurves in response to varying CPAP system requirements in a number ofways, used separately or in conjunction with one another. Generally,such tuning can be achieved by altering the ratio between the maximumgas flow area and the minimum gas flow area and/or altering theresistance of the movable portion 12 to movement as a function of thepressure of the gas. Thus, vent 10 can be tuned by 1) altering the pivotangle of the movable portion 12 with respect to the fixed portion 14 inthe relaxed position; 2) altering the ratio of the area of the orifice20 with respect to the outer periphery 18 of the movable portion 12; 3)altering the shape or size of the orifice 20 and/or outer periphery 18;4) changing the vent material to provide a different rigidity; 5)altering the thickness of the vent 10 to change rigidity; and/or 6)altering the cross-sectional area and/or configuration of the hinge 16to alter rigidity. Other methods can also be used to change the tuningof the vent, including, for instance, different heat treatmentprocedures for vents made of metal, etc.

In addition, one or more apertures of various shapes can be provided onthe movable portion 12 to alter the rigidity of the movable portion 12and/or alter a surface pressure gradient on the movable portion 12 whenexposed to the pressurized gas. Of course, if a desired minimum bleedflow is desired that is not provided for by the clearance between theorifice 20 and the outer periphery 18, one or more bleed orifices 24and/or 26 can be provided in the movable and fixed portions,respectively. Further, it is also contemplated that a multi-stage ventcould be provided by utilizing a plurality of movable portions withdifferent operating parameters in conjunction with respective fixedportion orifices or even to provide a second movable portion/orificecombination on the movable portion 12 itself. In any of thesealternatives, it may also be desirable to provide positive operatingstops on either the fixed or movable portions to positively limit travelof the movable portion in either direction. However, the use of positivestops may be avoided where their addition would increase noise (when thestops engage/disengage) to an extent that would be consideredundesirable.

In a preferred embodiment, the vent 10 is constructed from a unitarysheet of material such as stainless steel or other metal or plastic,although other materials exhibiting the desired combination of rigidity,flexibility, springiness and resistance to bending fatigue can also beused. In such an embodiment, the vent can be formed by stamping, lasercutting, water jet cutting, and molding or by other known methods. Inone preferred embodiment, the vent is cut from a single sheet of 0.1 mmthick polyester film of the type conventionally used for overheadprojector transparencies. Such film can be obtained from the Orbitcompany in Australia, as well as from other suppliers such as 3M andXerox. In this embodiment, the movable portion has an outer diameter of13 mm and the fixed portion has an outer diameter of 20 mm (althoughthis is not critical), with a gap between the movable and fixed portionsof 0.2 mm.

The shape of the vent need not be circular but can be any desired shape.The shape can even be asymmetrical so that it can only be positioned inthe base portion in the correct orientation, i.e., with the movableportion 12 pivoted toward the mask/gas supply tube in the relaxedposition and not toward the atmosphere. Alternatively, a correctorientation of the vent can be assured by providing an outer edge of thefixed portion with asymmetrically positioned notches or tabs to engagesimilarly positioned tabs/notches provided in the base portion. In analternative embodiment, the movable portion and fixed portion can beseparate components affixed to one another through use of a hinge oneither component or even through use of a separate hinge. In addition,the resistance of the movable portion to movement can be increased byutilization of an auxiliary spring member, which, in a simple form,could merely be an additional piece of rigid material overlaying andattached to the hinge 16. By providing a readily removable cover 40 overthe vent 10, the flow rate characteristics of the mask can be easily andinexpensively tailored to an individual's clinical need, merely byexchanging the vent 10 with an alternative vent 10 having differentoperating parameters. In addition interchangeable flaps and covers withorifices to atmosphere may be substituted so as to change operatingparameters.

The vent also need not be essentially flat, as in the presentembodiment, but can have different profiles as appropriate. Forinstance, the vent can have a convex or concave profile. Furthermore,the thicknesses of the movable portion and/or the fixed portion can beincreased and the edges of the orifice and/or movable portion can berounded to provide a smoother gas flow through the vent, with potentialgains in noise reduction. In one such embodiment, as shown in FIG. 9 inthe fully pressurized position, the rounded outer periphery 118 of themovable portion 112 of vent 110 can even overlap the rounded inner edgeof the orifice 120 in the fixed portion 114, with opposing surfaces ofthe two portions configured in a complementary manner to smooth airflowthrough the gap 122 therebetween. In such thicker, rounded embodiments,the movable and fixed portions would preferably be manufactured asseparate components and would be pivotally connected together by aseparate hinge that can be made of a different material. For instance,the movable and fixed portions 112 and 114 could be made of moldedplastic and the hinge 116 made of metal and attached to the othercomponents with adhesive. A small, polymeric bumper can be attached toone of the portions 112, 114 in the gap 122 to reduce noise should thetwo portions contact one another in the fully pressurized position.

In a preferred embodiment, the base and cover are made from machinegrade polycarbonate, preferably clear. Such material can be obtainedfrom the Dotmar company in Sydney. Australia. An alternative material isBayer Makrolon 2458 clear polycarbonate by Bayer AG. Other materialsfrom other suppliers can also be used.

FIG. 1 shows an exploded perspective view of an alternative embodimentof the flow regulation vent assembly. In this embodiment, a pin 62 thatis mounted or molded to the cover 40 contacts an edge of the movableportion 12 to push the movable portion open into the relaxed position.The pin 62 is preferably positioned at an edge of the movable portion 12approximately 30° around the perimeter of the movable portion 12 fromthe hinge 16. A tab 64 on the fixed portion 14 engaging a slot 66 on thecover 40 provides the correct rotational orientation of the movableportion 12 with respect to the pin 62. The height of the pin 62 isdetermined to provide the desired lift to the movable portion. The pin62 holds the movable portion in the open position until the pressure inthe mask starts to rise and the movable portion starts to close. Sincethe movable portion and hinge are relatively flexible the movableportion will bend and move toward the fully pressurized position. Inthis embodiment, the pin 62 prevents the movable portion from beingcompletely coplanar with the fixed portion in the fully pressurizedposition. Nonetheless, the effective flow area through the vent is stillreduced sufficiently to reduce the flow rate through the vent aspressure increases (as compared to a conventional fixed area vent). Anadvantage of this embodiment is that use of the pin 62 provides anexacting positioning of the movable portion in the open, relaxedposition, which can be important when making the vent from thin plastic.Thus, the movable portion need not be pre-formed to be in the open statebut can be pre-formed to be in a closed state, with the pin moving themovable portion to the open state. Another advantage of this embodimentis that the vent can be symmetrical from side to side so that eitherside can be placed toward the mask. In an alternative embodiment, thepin 62 can be replaced by a curved or sloped ramp.

Although the preferred embodiments discussed above utilize a movableportion that is positioned in the interior of the fixed portion, it iscontemplated that a reverse configuration can be used where the exteriorportion of the vent is movable and the interior portion is fixed to thebase portion or cover. It is also contemplated that different ventembodiments can be created utilizing different combinations ofalternative structures discussed herein. FIG. 10 shows a comparison ofthe performance of the preferred embodiment vent with conventionallyvented CPAP masks “A” and “B”. As can be seen, the conventional masks“A” and “B” have sharply increasing flow rate curves while a maskutilizing the vent of the present invention has a less steep flow ratecurve. Thus, at 16 cm H₂0, the mask utilizing the flow regulation ventof the present invention has a flow rate of approximately half of thelower limit flow rate of conventional mask “A” at 16 cm H₂0 and a flowrate of less than half of the average flow rate of conventional mask “B”at 16 cm H₂0.

Additional testing has shown that with a bilevel CPAP system such asVPAP II by ResMed Limited, a shortened rise time to the target maskpressure from when the patient begins inspiration is achieved using thepresent invention vent, as compared to a mask using a conventional fixedarea vent. If the rise time in pressure is too long, the patient has thefeeling of not getting sufficient air upon inhalation. Thus, a shorterrise time is preferred. In one test, the rise time for the presentinvention vent was approximately 250 ms, as compared to 300 ms in aconventional mask. Achieving the improved rise time performance byincorporating into a CPAP system the vent of the present invention is aless expensive alternative to achieving the same result by increasingflow generator performance.

Testing has also shown that in a CPAP mode where pressure in the mask isdesired to remain relatively constant, the present invention vent iseffective in doing so, as are conventional fixed flow area vents.Accordingly a vent of the present invention is compatible with constantpressure CPAP and may be used to ensure that a CPAP system deliversadequate exhaled gas wash out across the pressure range notwithstandingthat the pressure remains fixed for a given patient during a period oftreatment. Furthermore in a mode where the flow generator is shut off,testing has shown that the present invention vent acts as an effectiveanti-asphyxiation valve, providing pressure in the mask that issubstantially the same as if the mask was opened to the atmosphere byremoving the gas supply tube 34 from the mask. This is especiallyimportant in case of flow generator malfunction to reduce the risk ofasphyxiation, or even the perception thereof, by the patient.

The flow regulation vent of the present invention operates to reduce aflow area of the vent as pressure within the mask increases so as toreduce the flow rate of the vent as compared to a conventional fixedarea vent. This is accomplished by progressively moving a movableportion of the vent with respect to increasing pressure to progressivelyreduce a flow area between the movable portion of the vent and a fixedportion of the vent. The progressive movement of the movable portion canbe accomplished by applying a spring force to the movable portion toprogressively resist movement of the movable portion accompanying theincreasing pressure.

In a modification of the present invention, a strain gauge 60 can beoptionally attached by known means between the movable portion 12 andthe fixed portion 14 to determine a pivot angle between the movableportion 12 and fixed portion 14. See FIGS. 1-3. If the vent 10 isconstructed of plastic, the strain gauge can be embedded in the vent 10.The measurement of the pivot angle, taken in conjunction with theoperating parameters of the vent 10 and the pressure of the gas, canthen be used to calculate flow though the vent, thus allowing the ventto also function as a flow meter. Signals indicative of the pivot anglecan be processed in the vicinity of the vent, say by a processor locatedon the mask the gas supply conduit or headgear which secures the mask.Alternatively the processor may be located at a distance from the vent,say at the flow generator or in another location. In all instances thetransmission of the signals indicative of the pivot angle from thevicinity of the vent to the processor may be achieved by any suitablemeans such as by conductive wire, optical or wireless transmission.

An alternative embodiment of the present invention is shown in FIG. 12.In this embodiment, a flow regulation vent 150 includes a flexible flapportion 152 attached at a first end 156 to a fixed housing 154 so that afree end 158 of the flap 152 can move within a given range with respectto the housing 154. Thus, the flap acts as a cantilever arm with thefirst end 156 fixed and the free end 158 movable. The housing 154 isconnected to a mask shell or gas flow conduit. The vent housing 154 canbe a separate component attachable to the mask shell or gas flowconduit, or can be integrated with such components. A side 153 of theflap 152 is exposed to an interior chamber of the mask shell or gas flowconduit that is pressurized to a pressure different than the exterioratmospheric pressure when the mask is in use. A side 155 of the flap ispositioned toward an atmosphere side of the vent 150. The housing 154includes a vent orifice 160 positioned beneath the free end 158 of theflap 152. A portion of the housing 154 surrounding the vent orifice 160is curved to provide a surface 161 having a radius of curvature 162about a single axis. The flap 152 comes into contact with the housing154 at the surface 161. As shown in FIG. 12, the flap 152 is in arelaxed state such that the vent orifice 160 is completely uncovered anda gas flow area between the vent orifice 160 and the flap 152 is at amaximum.

While flexible, the flap 152 has a level of natural rigidity that willresist bending of the flap 152 and will provide a spring resistanceagainst bending of the flap. When the mask is in use, a force will actagainst this spring resistance of the flap 152 and cause the free end158 of the flap 152 to move toward the vent orifice 160. As the free end158 of the flap 152 moves closer to the vent orifice 160 with increasingmask pressure, it will follow the radius of curvature 162 of surface 161of the housing 154, progressively closing the vent orifice 160 andreducing the gas flow area between the vent orifice 160 and the flap152. The amount the flap 152 can move between the relaxed state and astate where the vent orifice 160 is completely covered is shown as amaximum deflection angle 164, measurable in degrees. As discussed withrespect to previous embodiments above, the interaction between theincreasing mask pressure and decreasing gas flow area acts to reduce thegas flow rate through the vent 150 as compared to standard fixed flowarea vents.

The vent 150 can be tuned to provide different relationships betweenmask pressure and gas flow area. Such tuning can be accomplished bychanging the thickness of the flap 152, the material the flap 152 ismade of, or the radius of curvature 162, where a larger radius willallow the flap 152 to progressively close the vent orifice 162 underlower mask pressures as compared to a smaller radius of curvature 162.The curved surface 161 is shown as being convex. However, in alternativeembodiments, a concave curved surface can also be used. FIG. 13 showsthe relationship between the radius of curvature and the deflectionangle for a given pressure at which the flap completely closes the vent.Although other radius of curvature and deflection angles can be used,the chart shows the radius of curvature to be greater than 21 mm andbetween 26 and 41 mm with the deflection angle between 15 and 25degrees. The flexing of a flap fixed at one end is governed by thefollowing equation:

1/r=L ² W/(2EI)  (Eq. 1)

-   -   Where:        -   r=radius of curvature        -   L=length of flap to deflect from an initial position to            closing of the vent orifice        -   W=uniform load per unit length (air pressure×surface            area/length)            -   W=Pb where                -   P=mask air pressure                -   b=flap width        -   E=modulus of elasticity of the flap material        -   I=section moment of inertia of the flap            -   I=bt³/12 where                -   t=flap thickness        -   L can be expressed in terms of arc radius and angle            -   L=ra where                -   a=deflection angle in radians

By substituting for L in Eq. 1 and solving for angle a, the followingequation for the deflection angle of the flap is derived:

a=(Et ³/6Pr ³)^(1/2)  (Eq. 2)

The vent 150 of this embodiment is intended for the use with a mask thatrequires a higher vent flow rate at low pressure. The vent 150 can bedesigned to work alone or in combination with a fixed bleed such as afixed flow area bleed orifice. Where the vent 150 operates alone, it ispreferably designed so that the flap 152 does not completely cover thevent orifice 160 and fully close the vent 150 under normal operatingconditions.

It is preferable that the flap 152 be constructed of a lightweightmaterial for fast response to pressure changes in the mask. However, thematerial must have sufficient stiffness to provide a spring bias againstpressure changes in the mask yet the working stress of the flap ispreferably designed to be below the endurance limit of the material toprevent fatigue failure from the repetitive alternating stress imposedby opening and closing the vent orifice. The strain is preferablydesigned to be below 1% at maximum deflection to prevent creep failure.The material thickness, material properties and the radius of curvatureof the housing mainly control the stress and strain of the flap 152 andone or more of these parameters can be altered to adjust the stress andstrain in the flap. The flap material is preferably made of a thin filmand of a grade acceptable for medical application. Tolerances in thematerial thickness are preferably less than 10% to reduce variability inperformance.

It is preferred that the curved surface 161 of the housing 154 be of ahigh finish of 8 micron or better and free of irregularities in order toachieve an airtight seal when the flap 152 is fully closed. The ventorifice 160 can be of any desired shape, including a rectangular windowor grouped series of smaller orifices. The use of a symmetrically shapedorifice of constant width and length, such as a rectangle, will make thereduction in cross-sectional area of the vent orifice more uniform asthe flap progressively closes the vent orifice. However, the use of anorifice of non-constant width and/or length can be used to specificallytailor the overall flow rate through the vent 150 as mask pressurechanges. Fillets of 0.5 mm minimum and draft angles of 3-6 degrees canbe used on the vent orifice 160 to reduce air noise.

One specific advantage of this embodiment as compared to known vents isthe ability and ease with which the flow characteristics of the vent canbe altered at specific pressures within the expected operating pressurerange. By altering the characteristics of the housing and flap asdiscussed above, the flow rate through the vent can be altered dependingon the pressure level.

For instance, in certain situations it may be desirable to quicklyreduce flow through the vent as pressure increases above a certainspecified pressure level. This can be accomplished by using a housing154 that has a curved surface 161 with an increasing radius of curvaturebeyond a point where the flap 152 would be expected to contact thecurved surfaced at the specified pressure level. See FIG. 46, where thecurved surface 161 of the housing 154 has a first radius of curvaturefrom a fixed end 156 of the flap 152 up to change point 165 and a largersecond radius of curvature beyond change point 165. With suchembodiments utilizing curved surfaces 161 with an increased radius ofcurvature beyond a change point, it will take smaller incrementalpressure increases above the specified pressure level to bring more ofthe flap 152 into contact with the curved surface 161 to close more ofthe orifice 160. Thus, a gas flow area between the flap 152 and thecurved surface 161 will decrease at a faster rate above the specifiedpressure level.

It is even contemplated that beyond the change point, some embodimentscould have flat surfaces 161, i.e., having an infinite radius ofcurvature. See FIG. 47. In such embodiments, the flap would come intocomplete contact with the curved surface above the specified pressurelevel, thereby closing the vent orifice 160 above the specified pressurelevel. In such an embodiment, venting above the specified pressure levelwould have to be through a fixed area bleed orifice on the flowregulation vent or mask assembly. It is also contemplated that theradius of curvature of the surface 161 could increase in discrete stepsbeyond a certain change point 165 or continuously increase beyond acertain change point 165. Under certain circumstances, the radius ofcurvature can be decreased beyond the change point 165 to provide anopposite effect where the rate of reduction of the gas flow area betweenthe flap 152 and the vent orifice 160 decreases beyond the change pointas the pressure increases.

A similar result can be achieved by reducing the cross-sectional area ofthe vent orifice 160 beyond the change point 165. See FIG. 48 where thewidth of the orifice 160 begins to decrease at change point 165 anddecrease further at second change point 167. In this embodiment, the gasflow area between the flap 152 and the vent orifice 160 will decrease atan increasing rate beyond change point 165 (associated with a firstspecified pressure level) and decrease at an even faster rate beyondsecond change point 167 (associated with a second specified pressurelevel). The change in width of the orifice 160 can be at one or morediscrete points, can be continuous within specified ranges or can beincreasing or decreasing within specified ranges. The change incross-sectional area of the vent orifice can also be accomplished bypositioning an insert of a desired width profile in the vent orifice 160to effectively alter the width of the vent orifice. As with the exampleabove, the opposite effect can also be accomplished by reducing a widthof the vent orifice 160 before the change point 165. Where the ventorifice 160 comprises a plurality of smaller spaced apart orifices, theeffect can be achieved by altering the area of one or more of theorifices with respect to the other orifices as they) are positionedfurther from the fixed end 156 of the flap 152.

A similar result can be achieved by reducing the thickness (and thusrigidity) of the flap 152 beyond a change point 169 on the flap 152. SeeFIG. 49. In this embodiment, the less rigid outer portion of the flap152 will flex more easily toward the curved surface 161 beyond changepoint 169 (associated with a specified pressure level) and close thevent orifice 160 at a faster rate. The opposite effect can be achievedby increasing the rigidity of the flap 152 as one or more pointsoutboard of the fixed end 156. The change in thickness can be at one ormore discrete points, can be continuous within specified ranges or canbe increasing or decreasing within specified ranges. Of course, therigidity of the flap 152 can be altered along its length in othermanners as well, such as by the use of an auxiliary stiffening rib ofvarying rigidity in conjunction with the flap 152 to achieve the sameresults.

One or more of these tuning mechanisms can be used in conjunction witheach other to readily and effectively provide an unlimited ability toprecisely tune the gas flow characteristics of the flow regulation vent150 at any point within an anticipated operating pressure range.

The flap can be attached to the housing by riveting, screwing, clamping,use of adhesive or other known methods. The flap can also be attached tothe housing by being positioned in a slot in the housing, the slotpreferably forming a friction fit between the housing and the flap.

In general, the vent of this embodiment will operate under the followingconditions. A large deflection angle will cause higher initial airflowthrough the vent, but will delay closure of the vent. A large radius ofcurvature will cause the flap to close at lower pressure. A large ventwill cause higher initial airflow and the size of the vent orifice islimited by the ability of the flap to seal the vent orifice with nodeformation. In masks utilizing a fixed area bleed vent, the end of theflap 152 can extend beyond the end of the vent orifice 160 in order tomaintain positive air pressure acting on the flap to keep it closed athigh pressure once it is shut. An overlap of 1 mm or greater isconsidered adequate. A bleed vent can be provided in the flow regulationvent by undercutting a portion of the surface 161 through to the ventorifice 160 such that the undercut potion can still flow gas to the ventorifice 160 even when the flap is in complete contact with the surface161. A bleed vent can also be provided by placing an orifice in the flap152 that allows gas to flow though the flap 152 to the orifice 160 evenwhen the flap 152 is in complete contact with the surface 161.

The flap 152 is preferably made of a material such as polyester film.The film can be slit to size, and then cut to length. Holes can bepunched in the film for location purposes. The housing is preferablymade of a moldable clear material for ease of cleaning and visibility.In a preferred embodiment, the vent 150 is detachable from the mask orgas flow conduit. This facilitates replacement in case of damage, theability to fine tune vent operation for specific applications and theability to upgrade with improved designs.

FIGS. 14-16 disclose an alternative embodiment of the vent 150 mountedto a swivel elbow joint 170 for connecting a gas flow conduit/tube to amask shell. FIGS. 14 and 15 are perspective views of the vent fromdifferent angles and FIG. 16 is a sectional view of the vent 150. Inthis embodiment, the vent 150 is constructed on a cover 172 used tocover a vent chamber housing 174 mounted on the swivel joint 170. Thevent 150 communicates with an interior of the swivel joint 170 and thus,the mask shell, via passage 182. The cover 172 includes snap arms 178for engaging slots 180 to hold the cover 172 on the housing 174,although other known attachment mechanisms can also be used for thispurpose. The vent 150 includes a flap 152, a vent orifice 160 and acurved surface 161 as in the embodiment of FIG. 12 (see FIG. 26). Inthis embodiment, the vent orifice 160 is rectangular. However, thisembodiment also includes a fixed bleed orifice 176 that remains open toprovide a minimum vent flow even when the flap 152 completely covers theorifice 160 and the vent 150 is closed. The vent 150 of this embodimentis detachable from the swivel joint 150 for replacement and/or cleaning.

FIGS. 17-26 disclose an alternative embodiment of the vent 150. In thisembodiment, the vent housing 154 is formed as a semi-circular clip thatcan detachably clip onto the swivel elbow joint 170. The vent 150communicates with an interior of the swivel joint 170 and thus, the maskshell, via passage 182. This embodiment includes two parallelrectangular vent orifices 160 and a plurality of circular fixed bleedorifices 176. Otherwise, the vent 150 of this embodiment operatessimilarly to the vent 150 of FIGS. 14-16.

FIGS. 19-20 disclose an alternative embodiment of the vent 150. In thisembodiment, the vent housing 154 is formed as a clip that can detachablyclip onto the swivel elbow joint 170. The vent 150 communicates with aninterior of the swivel joint 170 and thus, the mask shell, via passage182. This embodiment includes a single rectangular vent orifice 160 butdoes not include a fixed bleed orifice. Otherwise, the vent 150 of thisembodiment operates similarly to the vent 150 of FIGS. 14-16.

FIGS. 21-23 disclose alternative embodiments of the vent 150. In theseembodiments, the vent housing 154 is circular for detachable attachmentto a circular mount on a mask shell or gas flow conduit. In theembodiments of FIGS. 21 and 23, the vent orifice 160 is oval shaped. Inthe embodiment of FIG. 22, the vent orifice 160 is shaped as a series ofinterconnected channels. The embodiments of FIGS. 21 and 22 do notinclude fixed bleed orifices while the embodiment of FIG. 23 includes aplurality of fixed bleed orifices 176 that extend in parallel alongopposite sides of the orifice 160. In each of these embodiments, thevent orifice is formed on a cover 172 for attachment to the circularhousing 154, similarly to the embodiment of FIGS. 14-16. The housing 154can be provided with an orientation projection 184 for engaging a notch186 in the cover to rotationally orient the cover 172 with respect tothe housing 154. Otherwise, the vent 150 of these embodiments operatessimilarly to the vent 150 of FIGS. 14-16.

FIG. 24 discloses an embodiment of a vent 150 similar to the embodimentof FIGS. 14-16, as well as disclosing how the swivel elbow joint 170 isattached to a mask shell 190 of known construction. Mask shell 190includes a pair of parallel ports 192 that are in fluid communicationwith the mask interior.

FIGS. 25-27 disclose an alternative embodiment of the vent 150 where thevent housing 154 is generally rectangular in shape and includes a pairof mounting bosses 194 adapted to engage the pair of parallel flow ports192 (see FIG. 24) to allow flow from an interior of the mask shell 190to the vent 150. The mounting bosses are sized and configured to beretained on the flow ports 192 by a friction fit, although other knownretention mechanisms can also be used. Since the mask shell 190 is of aknown design in current production (Ultra MIRAGE® by ResMed Limited),the configuration of this embodiment allows the easy retrofitting ofthat known mask with the variable vent of the present invention. Thehousing 154 includes a plurality of internal ribs 196 and seating pads202 for engaging and positioning a diffuser 198 within the housing 154.As shown in FIG. 27, when the diffuser 198 is properly positioned in thehousing 154, a gas chamber 206 is formed that is in communication withpassages 204 in bosses 194, which are in turn, in communication with theinterior of the mask shell via flow ports 192. The diffuser 198 includesa plurality of orifices 200 through which gas in chamber 206 can pass toflow toward the vent orifice 160. The plurality of spaced-apart orifices200 acts to diffuse the gas flow from the two passages 204 to moreevenly act on the flap 152.

The diffuser 198 also includes a pair of extending retaining walls 208for engaging a center portion of the flap 152 to position the flap 152against the convex curved surface 161 of the cover 172. In thisembodiment, the flap 152 is not attached to the cover 172 at one of itsends, but rather, flexes from its center to, in effect, create twointerconnected flaps 152. The cover 172 includes a centrally locatedprojecting pin 212 to engage a centrally located positioning bore 210 onthe flap 152 to position the flap 152 with respect to the cover 172 andprevent lateral movement of the flap 152. The internal ribs 196 of thehousing 154 are positioned alongside the flap 152 to prevent the flap152 from rotating within the housing 154. In an alternative embodiment,the bore 210 and pin 212 can have an asymmetrical configuration toprevent rotation of the flap 152. The flap 152 can also be staked orriveted to the cover 172. The vent cover can be retained to the housingby a snap fit, friction fit, adhesive or other known retentionmechanism. The vent cover 172 includes a vent orifice 160 in the form ofa plurality of spaced-apart round orifices. This embodiment does notinclude a fixed bleed orifice but such a fixed bleed orifice can beprovided on the vent 150 or elsewhere on the mask shell or gas flowconduit. Otherwise, the vent 150 of this embodiment operates similarlyto the vent 150 of FIGS. 14-16, with each outboard side of the flap 152movable in response to mask pressure to progressively close a respectiveportion of the vent orifice 160.

FIG. 28 shows a cover 172 and mounted flap 152 of a configurationsimilar to the configuration shown in FIGS. 25-27, with the flap 152 inthree different positions based on mask pressure exposed to the flap152. In the first position, the flap 152 is entirely open. In the secondposition, increased mask pressure has moved the outboard ends of theflap 152 toward the convex curved surface 161 of the vent cover 172 topartially obstruct flow through the vent orifices 160. In the thirdposition, mask pressure has increased to the point that the outboardends of the flap 152 have moved further toward the curved surface 161 tocompletely close the vent orifices 160. All of the embodiments shown inFIGS. 12-32 operate similarly.

FIG. 29 discloses a mask shell of the type shown in FIG. 24 with a vent150 similar to the type disclosed in FIGS. 25-28 attached to the flowports 192. In this embodiment, the vent orifice 160 is configured as twooval orifices.

FIGS. 30-32 disclose an embodiment similar to the embodiment disclosedin FIGS. 25-29 but where the curved surface 161 on cover 172 is concave.In this embodiment, the housing 154 includes a plurality of raised walls220 connected to an internal floor of the housing 154 to both supportthe flap 152 and to diffuse air/gas flow from passages 204. The ventcover 172 also includes a plurality of raised posts 222 surrounding thecurved surface 161 to position and retain the flap 152 over the curvedsurface 161. The walls 220 and posts 222 interact to maintain the flap152 in the desired position over the curved surface 161 when the ventcover 172 is installed on the housing 154, as can be best seen in FIG.32. In the embodiments shown in FIGS. 12-29, the flap 152 is fixed atits center and the outboard ends of the flap 152 move over the convexcurved surface 161 to vary the vent orifice 160. In this embodimenthowever, the curved surface is 161 is concave and the flap 152 is notfixed to the vent cover 172 at any point. As opposed to the previousembodiments where the flap bends from one fixed end or from the center,in this embodiment, the flap 152 bends from both outboard ends 224 suchthat the flap center 226 bows toward the concave curved surface 161under increasing mask pressure to progressively close the vent orifice160. This embodiment also includes a fixed bleed orifice 176.

FIGS. 33 and 34 show two charts comparing the flow performance of astandard ResMed™ Mirage® mask with a ResMed™ Mirage® mask utilizing avent according to one of the embodiments of FIGS. 12-32. In FIG. 37 thechart shows the flow performance of the mask utilizing a vent 150(including a fixed bleed orifice 176) as compared to the standard mask.The flow rate for the inventive mask is substantially higher at low maskpressures but tapers off at higher mask pressures to be only slightlyhigher than the standard mask. In effect, the closing of the variablevent 150 is delayed somewhat as shown by the hump in the curve at lowermask pressures. This delayed closure can be achieved by utilizing acurved surface 161 with a smaller radius of curvature or a thicker,stiffer flap 152.

FIG. 34 shows a comparison between a standard ResMed™ Mirage® mask witha ResMed™ Mirage® mask utilizing a vent according to one of theembodiments of FIGS. 12-32. The solid curve is for the standard mask.The box curve is for a mask continuing to utilize the fixed bleedorifices of the standard mask but also using a variable vent 150 (havingno fixed bleed orifice). This curve shows a higher flow rate at lowermask pressures when the variable vent 150 is open but then overlays thestandard curve once the variable vent 150 is closed and flow is onlythrough the fixed bleed orifices of the standard mask. The initial humpin the curve was achieved by using a larger flap deflection angle 164 of22 degrees and a larger radius of curvature 162 of curved surface 161 of35 mm. The diamond curve is for a mask utilizing only the variable vent150, with no fixed bleed orifice in the vent 150 or the mask. Thiscurves shows flow at lower mask pressures that decreases as maskpressure rises until the vent 150 completely closes and there is no flowat all.

The flow regulation vent of the present invention is simple andinexpensive to manufacture, especially when cut made from a flat,unitary disk as described above, but provides effective, easily tailoredflow regulation. With such an effective flow regulation vent, the flowgenerator is delivering higher pressure and need not be sized to havethe additional capacity to handle increased flow rates at higherpressures, as with conventional CPAP systems. Noise from the flowgenerator motor can also be reduced since the motor can operate at lowerRPM to deliver the reduced volume of high pressure airflow. The ventalso acts as a sound barrier, reducing the level of noise from theinterior of the mask, including noise created by the flow generator thatescapes to the atmosphere. Further, the reduced flow rate at highpressure results in less noise generation from the airflow itself. Thevent also reduces rebreathing of C0₂ and provides for faster airpressure rise time, increasing the effectiveness of the CPAP treatment.Each of these benefits promotes patient compliance with CPAP treatment.

FIGS. 35-42 show an alternative embodiment of the present invention. Aflow regulation vent 250 includes a generally round flap portion 252 anda generally tubular fixed housing portion 254. The fixed housing portion254 includes a user side 256 adapted to be connected to a mask and aflow generator side 258 adapted to be connected to a pressurized supplyof gas from a flow generator to position the flow regulation vent 250between the mask and the flow generator. The fixed housing portion 254further includes a primary vent orifice 260 positioned near the userside of the housing and a secondary vent orifice 262 positioned near theflow generator side of the housing 254, each flowingly connected to anexhaust orifice 264 (see FIG. 38) exposed to the atmosphere to allow gasflow between each of the primary vent orifice 260 and secondary ventorifice 262 and the exhaust orifice 264. In the embodiment shown, thesecondary vent orifice 262 is in the form of a plurality of smallerorifices 266 but can also have other configurations, as discussed above.See FIG. 37. The secondary vent orifice 262 is positioned on a curvedsurface 274 of the fixed housing portion 254 and is adapted to engage amovable portion 278 of the flap portion 252.

The fixed housing portion 254 also includes a flap seating flange 268,against which a fixed portion 276 of the flap portion 252 seats and aprojecting orientation pin 270 for engaging an orientation orifice 272in the flap portion 252 for properly orienting the flap portion 252 withrespect to the fixed housing portion 254 when the flow regulation vent250 is assembled. A hinge portion 280 connects the movable portion 278of the flap portion 252 to the fixed portion 276. In the preferredembodiment, a radially outer portion of the curved surface 274 generallysmoothly transitions to the flap seating flange 268 to provide acontinuous surface against which the movable flap portion 278 can engageas it moves from a relaxed position to a flexed position.

The vent 250 of this embodiment operates as follows, with specialreference being made to FIGS. 40-42. FIG. 40 shows the vent 250 duringinhalation by the user. The air flow from the flow generator (shown asupward pointing arrows in the Figure) has overcome a natural springforce of the flap 252 to move the movable portion 278 of the flap 252toward the user, increasing a flow area between the movable portion 278and the fixed portion 276 of the flap 252. This allows ample air flow tothe user during inhalation and prevents any feeling of asphyxiation. Themovement of the movable portion 278 has also brought more of the movableportion 278 into contact with more of the curved surface 274 andprogressively reduced a flow area between movable portion 278 and thecurved surface 274 to reduce flow through the secondary vent orifice262. This reduces a total flow area through vent orifices 262 and 260 toreduce flow through the exhaust orifice 264 from air flow from the flowgenerator or from exhalation.

During exhalation, as shown in FIG. 41, the spring force of the flap 252has returned the movable portion 278 of the flap 252 to a relaxedposition, minimizing the flow area through the flap 252. This acts as anon-rebreathing mechanism, minimizing any exhalation into the flowgenerator conduit and creating CO₂ buildup there that will be rebreathedby the user and similarly acts as a one-way valve to prevent oxygen fromgoing back into the flow generator conduit should the flow generatorstop working due to malfunction. This also minimizes any incoming gasflow from the flow generator during exhalation. The movement of themovable portion 278 has also uncovered the secondary vent orifice 262flow area to add that area to that of the flow area of primary ventorifice 260 and increase a total outflow area of the vent 250 for theexhalation gases. With the increased total outflow area, as well as lessflow through the total outflow area due to inflow from the flowgenerator, the exhalation gases can exit the mask at a greater flowrate. This increases CO₂ outflow from the mask and decreases undesirableCO₂ buildup in the mask. The vent 250 also results in lower maskpressure during exhalation as a result of the increased total outflowarea and decreases the pressure rise time in the mask, as compared toconventional masks.

As shown in FIG. 42, the vent 250 also acts effectively as ananti-asphyxia valve in the event that the flow generator ceasesoperation. In such a situation, the movable portion 278 of the flap 252remains in the relaxed, closed position, keeping the secondary ventorifice 262 open and increasing the total flow area (in combination withprimary vent orifice 260) for allowing outside air into the mask duringinhalation by the user. The vent 250 eliminates the need for providingother vents on the mask itself.

An alternative configuration of the flow regulation vent 250 is shown inFIGS. 43-45. In this configuration, the housing 254 is relatively narrowso that it can be inserted into a slot 284 in a swivel elbow joint 270.The flap 252 is somewhat T-shaped with the movable portion 278 of theflap 252 being a relatively large proportion of the flap 252 and thefixed portion 276 of the flap 252 being a relatively small proportion ofthe flap 252. In this configuration, the flap 252 is held in place withrespect to the housing 254 by a flap cover plate 286 that attaches tothe housing 254 and sandwiches the fixed portion 276 therebetween. Thecover plate can also be configured to contact a flow generator side ofthe movable portion 278 when in the relaxed position to prevent reverseflow from exhalation into the flow generator conduit. In thisembodiment, the secondary vent orifice 262 is generally rectangular andis not positioned on a curved surface of the housing 254. This is not asimportant with the flow regulation vent 250 as it is in previousembodiments, since it is not as important to have a progressivelyincreasing or decreasing flow area through the vent orifice 262. Rather,it is more important that the flow area through the vent orifice 262 besmall during inhalation and large during exhalation. This embodimentotherwise operates as does the embodiment of FIGS. 35-42. An exhalationflow deflector 288 can be attached to the elbow joint 270 to direct theflow of exhalation gas outside the mask. See FIG. 45. The flap coverplate can be attached to the housing 254 by welding, adhesive, snap fitor other known attachment methods.

In the preferred embodiment, the flap 252 is constructed from thinpolyester sheet with a flap diameter of 21.5 mm (positioned in a housinginside diameter of 23 mm), a flap thickness of 0.004 inch and a flaphinge width of 7 mm. The flow characteristics through the vent 250 canbe tailored as desired by altering the flap characteristics, includingthickness, movable portion area, material and hinge width. A fixed areaorifice can also be provided through the vent 250 between the flowgenerator and the mask to provide flow from the flow generator shouldthe movable portion 278 of the flap become stuck closed. As withembodiments discussed above, the vent 250 can operate as a flow meter bymeasuring a pressure drop across the vent 250 or by measuring anelectrical signal from a strain gauge attached to the flap 252. Theorifice 260 can also be configured to provide a high resistance toinflow and a low resistance to outflow.

It is intended that various aspects of the embodiments discussed abovecan be used in different combinations to create new embodiments of thepresent invention.

It will be apparent to those skilled in the art that variousmodifications and variations may be made without departing from thescope of the present invention. Thus, it is intended that the presentinvention covers the modifications and variations of the invention.

1-20. (canceled)
 21. A flow regulation vent for use in controlling avent flow of washout gas in a system for supplying breathable gaspressurized to within a therapeutic pressure range above atmosphericpressure to a patient in the treatment of a sleep disordered breathingcondition, the flow regulation vent comprising: a housing having atleast one vent orifice and at least one fixed bleed orifice; and a flapconfigured to regulate the vent flow of washout gas through the at leastone vent orifice, wherein the at least one fixed bleed orifice is notcovered by the flap in any position and the flow regulation ventprovides a minimum vent flow independent of the position of the flap.22. The flow regulation vent of claim 21, wherein the flap is configuredsuch that increasing the pressure of the breathable gas within thetherapeutic pressure range causes the flap to move and reduce across-sectional area of the at least one vent orifice to reduce the ventflow through the at least one vent orifice.
 23. The flow regulation ventof claim 22, wherein the vent flow through the at least one fixed bleedorifice increases in response to a reduction of the vent flow throughthe at least one vent orifice such that the vent flow through the atleast one vent orifice and the at least one fixed bleed orifice issubstantially constant when the breathable gas is pressurized within thetherapeutic pressure range.
 24. The flow regulation vent of claim 21,wherein the therapeutic pressure range is 4 cmH₂O to 30 cmH₂O.
 25. Theflow regulation vent of claim 21, wherein the housing further comprisespositive operating stops to limit travel of the flap.
 26. The flowregulation vent of claim 21, wherein the at least one vent orifice ispositioned downstream of the flap relative to the vent flow.
 27. Theflow regulation vent of claim 21, wherein the flap extends from thehousing such that the flap is cantilevered over the at least one ventorifice.
 28. The flow regulation vent of claim 21, further comprising adiffuser to diffuse the vent flow.
 29. The flow regulation vent of claim21, wherein the flap has an outer diameter that is greater than athickness of the flap.
 30. The flow regulation vent of claim 21, whereinat least one vent orifice comprises a plurality of vent orifices and theat least one fixed bleed orifice comprises a plurality of fixed bleedorifices.
 31. The flow regulation vent of claim 21, wherein the flapcomprises an elastically deformable material.
 32. The flow regulationvent of claim 31, wherein when the flap is not elastically deformed, theflap is configured to not restrict the vent flow through the at leastone vent orifice.
 33. The flow regulation vent of claim 32, wherein whenthe breathable gas is pressurized to a within pressure within thetherapeutic pressure range above atmospheric pressure, the flap isconfigured to be elastically deformed by the pressure of the breathablegas.
 34. The flow regulation vent of claim 33, wherein the flap isconfigured to elastically deform due to an increase in the pressure ofthe breathable gas to reduce a cross-sectional area through the at leastone vent orifice.
 35. A respiratory therapy system for supplyingbreathable gas pressurized to within the therapeutic pressure rangeabove atmospheric pressure to a patient in the treatment of a sleepdisordered breathing condition, the respiratory therapy systemcomprising: a mask configured to provide the breathable gas to thepatient's airways; a flow generator configured to pressurize thebreathable gas; a conduit configured to provide the breathable gas fromthe flow generator to the mask; and the flow regulation vent of claim21.
 36. The respiratory therapy system of claim 35, wherein the flowregulation vent is positioned integrally along the conduit.
 37. Therespiratory therapy system of claim 36, wherein the conduit comprises acircular mount and the housing is circular for attachment to thecircular mount.
 38. The respiratory therapy system of claim 35, whereinthe flow regulation vent is not positioned on the mask.
 39. A maskconfigured to provide breathable gas pressurized to within thetherapeutic pressure range above atmospheric pressure to the patient'sairways in the treatment of a sleep disordered breathing condition, themask comprising: a shell configured to cover the mouth and/or thenostrils of the patient; an elbow joint having a first end configured tobe removably and rotatably connected to the shell and a second endconfigured to be removably connected to a conduit to receive thebreathable gas from a flow generator; and the flow regulation vent ofclaim 21, wherein the flow regulation vent is integrated with the elbowjoint such that the elbow joint and the flow regulation vent areremovable from the shell together.
 40. A flow regulation vent for use incontrolling a vent flow of washout gas in a system for supplyingbreathable gas pressurized to within a therapeutic pressure range aboveatmospheric pressure to a patient in the treatment of a sleep disorderedbreathing condition, the flow regulation vent comprising: a fixedportion having at least one vent orifice and at least one fixed bleedorifice; and a movable portion positioned adjacent to the fixed portionand configured to be moved by pressure of the breathable gas to regulatethe vent flow of washout gas through the at least one vent orifice suchthat in any position the movable portion does not cover the at least onefixed bleed orifice to provide a minimum vent flow independent of theposition of the movable portion.
 41. The flow regulation vent of claim40, wherein the movable portion comprises an elastically deformablematerial.
 42. The flow regulation vent of claim 41, wherein when themovable portion is not elastically deformed, the movable portion isconfigured to not restrict the vent flow through the at least one ventorifice.
 43. The flow regulation vent of claim 42, wherein when thebreathable gas is pressurized to a within pressure within thetherapeutic pressure range above atmospheric pressure, the movableportion is configured to be elastically deformed by the pressure of thebreathable gas.
 44. The flow regulation vent of claim 43, wherein themovable portion is configured to elastically deform due to an increasein the pressure of the breathable gas to reduce a cross-sectional areathrough the at least one vent orifice.
 45. The flow regulation vent ofclaim 40, wherein the therapeutic pressure range is 4 cmH₂O to 30 cmH₂O.46. The flow regulation vent of claim 40, wherein the fixed portionfurther comprises positive operating stops to limit travel of themovable portion.
 47. A respiratory therapy system for supplyingbreathable gas pressurized to within the therapeutic pressure rangeabove atmospheric pressure to a patient in the treatment of a sleepdisordered breathing condition, the respiratory therapy systemcomprising: a mask configured to provide the breathable gas to thepatient's airways; a flow generator configured to pressurize thebreathable gas; a conduit configured to provide the breathable gas fromthe flow generator to the mask; and the flow regulation vent of claim40.
 48. The respiratory therapy system of claim 47, wherein the flowregulation vent is positioned integrally along the conduit.
 49. Therespiratory therapy system of claim 48, wherein the conduit comprises acircular mount and the fixed portion is circular for attachment to thecircular mount.
 50. A mask configured to provide breathable gaspressurized to within the therapeutic pressure range above atmosphericpressure to the patient's airways in the treatment of a sleep disorderedbreathing condition, the mask comprising: a shell configured to coverthe mouth and/or the nostrils of the patient; an elbow joint having afirst end configured to be removably and rotatably connected to theshell and a second end configured to be removably connected to a conduitto receive the breathable gas from a flow generator; and the flowregulation vent of claim 40, wherein the flow regulation vent isintegrated with the elbow joint such that the elbow joint and the flowregulation vent are removable from the shell together.